Conveyance device, conveyance system, and head control method

ABSTRACT

A conveyance device includes a conveyor to convey a conveyed object, a head unit to perform an operation on the conveyed object, a sensor to obtain surface data of the conveyed object, provided for each head unit, and at least one processor. The processor is configured to calculate a first detection result including at least one of a position, a speed of movement, and an amount of movement of the conveyed object based on the surface data, set a detection area based on the first detection result, calculate a second detection result using the detection area according to the first detection result. The processor is further configured to control operation of the at least one head unit based on the second detection result.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority pursuant to 35U.S.C. § 119(a) to Japanese Patent Application Nos. 2017-027481, filedon Feb. 17, 2017, and 2018-016719, filed on Feb. 1, 2018, in the JapanPatent Office, the entire disclosure of each of which is herebyincorporated by reference herein.

BACKGROUND

Technical Field

This disclosure relates to a conveyance device, a conveyance system, anda head controlling method.

Description of the Related Art

There are various types of operation using a head. For example, thereare image forming methods that include discharging ink from a print head(so-called inkjet method). In an apparatus including a head to performan operation on an object being convened (i.e., a conveyed object), ifthe timing of the operation is improper or the position of the conveyedobject deviates from a reference position, the outcome of the operationmay include a deviation or misalignment.

SUMMARY

According to an embodiment of this disclosure, a conveyance deviceincludes a conveyor to convey a conveyed object in a conveyancedirection, at least one head unit to perform an operation on theconveyed object, a sensor to obtain surface data of the conveyed object,provided for each head unit, and at least one processor configured asfollows. The processor is configured to calculate a detection resultincluding at least one of a position, a speed of movement, and an amountof movement of the conveyed object based on the surface data obtained bythe sensor; and set a detection area used in calculation of thedetection, based on the detection result. The detection result includesa first detection result calculated using the detection area accordingto initial setting, and a second detection result calculated using thedetection area according to the first detection result. The processor isfurther configured to control operation of the head unit based on thesecond detection result.

According to another embodiment, a conveyance system includes aplurality of conveyance devices. Each of the plurality of conveyancedevices includes a conveyor to convey a conveyed object in a conveyancedirection, at least one head unit to perform an operation on theconveyed object, and a sensor to obtain surface data of the conveyedobject, the sensor provided for each head unit. The conveyance systemfurther includes at least one processor configured to calculate adetection result including at least one of a position, a speed ofmovement, and an amount of movement of the conveyed object based on thesurface data obtained by the sensor; and set a detection area used incalculation of the detection result, based on the detection result. Thedetection result includes a first detection result calculated using thedetection area according to initial setting, and a second detectionresult calculated using the detection area according to the firstdetection result. The processor is further configured to controloperation of at least one head unit based on the second detectionresult.

Yet another embodiment provides a method for controlling a head unit toperform an operation on a conveyed object. The method includes obtainingsurface data of the conveyed object; and calculating a first detectionresult including at least one of a position, a speed of movement, and anamount of movement of the conveyed object based on the surface data. Thefirst detection result is calculated using a detection area according toinitial setting. The method further includes setting, based on the firstdetection result, a detection area used to calculate a second detectionresult including at least one of the position, the speed of movement,and the amount of movement of the conveyed object; calculating thesecond detection result using the detection area according to the firstdetection result; and controlling operation of the head unit based onthe second detection result.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic view of a liquid discharge apparatus according toan embodiment;

FIG. 2 is a schematic view illustrating a general structure of theliquid discharge apparatus illustrated in FIG. 1;

FIG. 3 is a schematic view illustrating an example structure of theliquid discharge apparatus illustrated in FIG. 1;

FIG. 4 is a block diagram of a hardware configuration to calculatedisplacement of a conveyed object, according to an embodiment;

FIGS. 5A and 5B are schematic views of an external shape of a liquiddischarge head unit according to an embodiment;

FIG. 6 is a schematic block diagram illustrating a hardwareconfiguration to implement a conveyed object detector according to anembodiment;

FIG. 7 is an external view of a sensor device included in the conveyedobject detector illustrated in FIG. 6;

FIGS. 8A and 8B are schematic block diagrams of a functionalconfiguration of the conveyed object detector, according to anembodiment;

FIG. 9 is a diagram of a method of correlation operation according to anembodiment;

FIG. 10 is a graph for understanding of a peak position searched in thecorrelation operation illustrated in FIG. 14;

FIG. 11 is a diagram of example results of correlation operationaccording to an embodiment;

FIGS. 12A and 12B are plan view of a recording medium being conveyed;

FIG. 13 is a plan view of the recording medium being conveyed andillustrates creation of an image out of color registration;

FIG. 14 is a schematic block diagram of a hardware configuration of acontroller according to an embodiment;

FIG. 15 is a block diagram of a hardware configuration of a datamanagement unit of the controller illustrated in FIG. 9;

FIG. 16 is a block diagram of a hardware configuration of an imageoutput device of the controller illustrated in FIG. 9;

FIG. 17 is a flowchart of operation performed by the liquid dischargeapparatus illustrated in FIG. 3;

FIG. 18 illustrates an initial setting of a detection area detected bythe liquid discharge apparatus, according to an embodiment;

FIG. 19 illustrates an example of skew of the recording medium.

FIG. 20 illustrates setting of a second detection area by the liquiddischarge apparatus, according to an embodiment;

FIG. 21 illustrates setting of an irradiated area performed by theliquid discharge apparatus, according to an embodiment;

FIG. 22 illustrates setting of a third detection area by the liquiddischarge apparatus, according to an embodiment;

FIG. 23 illustrates setting of a fourth detection area by the liquiddischarge apparatus, according to an embodiment;

FIG. 24 is a timing chart of calculation of the amount of displacementof the conveyed object, according to an embodiment;

FIG. 25 is a schematic view of a liquid discharge apparatus according toVariation 1;

FIG. 26 is a schematic diagram of a conveyance device according toVariation 2; and

FIG. 27 is a schematic diagram of a liquid discharge apparatus accordingto Variation 3.

The accompanying drawings are intended to depict embodiments of thepresent invention and should not be interpreted to limit the scopethereof. The accompanying drawings are not to be considered as drawn toscale unless explicitly noted.

DETAILED DESCRIPTION

In describing embodiments illustrated in the drawings, specificterminology is employed for the sake of clarity. However, the disclosureof this patent specification is not intended to be limited to thespecific terminology so selected, and it is to be understood that eachspecific element includes all technical equivalents that operate in asimilar manner and achieve a similar result.

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views thereof,and particularly to FIG. 1, an image forming apparatus according to anembodiment of this disclosure is described. As used herein, the singularforms “a”, “an”, and “the” are intended to include the plural forms aswell, unless the context clearly indicates otherwise.

The suffixes Y, M, C, and K attached to each reference numeral indicateonly that components indicated thereby are used for forming yellow,magenta, cyan, and black images, respectively, and hereinafter may beomitted when color discrimination is not necessary.

General Configuration

Descriptions are given below of an embodiment in which a head unit of aconveyance device is a liquid discharge head unit, and an operationposition is a position at which the liquid discharge head unitdischarges liquid onto a web (a recording medium). When the head unit ofthe conveyance device is a liquid discharge head unit to dischargeliquid, the conveyance device is a liquid discharge apparatus.

FIG. 1 is a schematic view of a liquid discharge apparatus according toan embodiment, which discharges recording liquid such as aqueous ink oroil-based ink. Descriptions of embodiments are given below using animage forming apparatus as an example of the liquid discharge apparatus.

A liquid discharge apparatus 110 illustrated in FIG. 1 conveys aconveyed object such as a web 120. In the illustrated example, theliquid discharge apparatus 110 includes a roller 130 and the like toconvey the web 120, and discharges liquid onto the web 120 to form animage thereon. When an image is formed on the web 120 (i.e., a conveyedobject), the web 120 is considered as a recording medium. The web 120 isa so-called continuous sheet. That is, the web 120 is, for example, arolled sheet to be reeled.

For example, the liquid discharge apparatus 110 is a so-calledproduction printer. The description below concerns an example in whichthe roller 130 adjusts the tension of the web 120 and conveys the web120 in a conveyance direction 10. Hereinafter, unless otherwisespecified, “upstream” and “downstream” mean those in the conveyancedirection 10. A direction orthogonal to the conveyance direction 10 isreferred to as an orthogonal direction 20 (e.g., a width direction ofthe web 120). In the illustrated example, the liquid discharge apparatus110 is an inkjet printer to discharge four color inks, namely, black(K), cyan (C), magenta (M), and yellow (Y) inks, to form an image on theweb 120.

FIG. 2 is a schematic view illustrating a general structure of a liquiddischarge apparatus according to an embodiment. As illustrated in FIG.2, the liquid discharge apparatus 110 includes four liquid dischargehead units 210 (210Y, 210M, 210C, and 210K) to discharge the four inks,respectively.

Each liquid discharge head unit 210 discharges the ink onto the web 120conveyed in the conveyance direction 10. The liquid discharge apparatus110 includes two pairs of nip rollers, a roller 230, and the like, toconvey the web 120. One of the two pairs of nip rollers is a first niproller pair NR1 disposed upstream from the liquid discharge head units210 in the conveyance direction 10. The other is a second nip rollerpair NR2 disposed downstream from the first nip roller pair NR1 and theliquid discharge head units 210 in the conveyance direction 10. Each niproller pair rotates while nipping the conveyed object, such as the web120, as illustrated in FIG. 2. The nip roller pairs and the roller 230together serve as a conveyor to convey the conveyed object (e.g., theweb 120) in a predetermined direction.

The recording medium such as the web 120 is preferably a long sheet.Specifically, the recording medium is preferably longer than thedistance between the first nip roller pair NR1 and the second nip rollerpair NR2. The recording medium is not limited to webs. For example, therecording medium can be a folded sheet (so-called fanfold paper orZ-fold paper).

In the structure illustrated in FIG. 2, the liquid discharge head unitsare arranged in the order of black, cyan, magenta, and yellow in theconveyance direction 10. Specifically, a liquid discharge head unit 210Kfor black is disposed extreme upstream, and a liquid discharge head unit210C for cyan is disposed next to the liquid discharge head unit 210K.Further, the liquid discharge head unit 210M for magenta is disposednext to the liquid discharge head unit 210C for cyan, and the liquiddischarge head unit 210Y for yellow is disposed extreme downstream inthe conveyance direction 10.

Each liquid discharge head unit 210 discharges the ink to apredetermined position on the web 120, according to image data. Theposition at which the liquid discharge head unit 210 discharges ink(hereinafter “ink discharge position”) is almost identical to theposition at which the ink discharged from the liquid discharge head(e.g., 210K-1, 210K-2, 210K-3, or 210K-4 in FIG. 5A) lands on therecording medium (hereinafter “landing position”). In other words, theink discharge position can be directly (or almost directly) below theliquid discharge head unit. In the description below, the ink dischargeposition serves as an operation position of the liquid discharge headunit.

In the present embodiment, black ink is discharged to the ink dischargeposition of the liquid discharge head unit 210K (hereinafter “black inkdischarge position PK”). Similarly, cyan ink is discharged at the inkdischarge position of the liquid discharge head unit 210C (hereinafter“cyan ink discharge position PC”). Magenta ink is discharged at the inkdischarge position of the liquid discharge head unit 210M (hereinafter“magenta ink discharge position PM”). Yellow ink is discharged at theink discharge position of the liquid discharge head unit 210Y(hereinafter “yellow ink discharge position PY”). Note that, forexample, a controller 520 operably connected to the liquid dischargehead units 210 controls the respective timings of ink discharge of theliquid discharge head units 210 and actuators AC1, AC2, AC3, and AC4(collectively “actuators AC”) illustrated in FIG. 3, to move the liquiddischarge head units 210. In one embodiment, the timing control and theactuator control is performed by two or more controllers (or controlcircuits). The actuators AC serve as head moving devices and aredescribed later.

In the illustrated structure, each liquid discharge head unit 210 isprovided with a plurality of rollers. As illustrated in the drawings,the plurality of rollers includes, for example, the rollers respectivelydisposed upstream and downstream from each liquid discharge head unit210. Specifically, each liquid discharge head unit 210 is provided withone roller (i.e., a first roller) to support the web 120, disposedupstream from the ink discharge position and another roller (i.e., asecond roller) to support the web 120, disposed downstream from the inkdischarge position, in the conveyance passage along which the web 120 isconveyed.

Disposing the first roller and the second roller for each ink dischargeposition can suppress fluttering of the recording medium conveyed. Forexample, the first roller and the second roller are driven rollers.Alternatively, the first roller and the second roller may be driven by amotor or the like.

Note that, instead of the first and second rollers that are rotatorssuch as driven rollers, first and second supports that are not rotatableto support the conveyed object can be used. For example, each of thefirst and second supports can be a pipe or a shaft having a round crosssection. Alternatively, each of the first and second supports can be acurved plate having an arc-shaped face to contact the conveyed object.In the description below, the first and second supporters are rollers.

Specifically, a first roller CR1K is disposed upstream from the blackink discharge position PK in the conveyance direction 10 in which theweb 120 is conveyed. A second roller CR2K is disposed downstream fromthe black ink discharge position PK in the conveyance direction 10.

Similarly, a first roller CR1C and a second roller CR2C are disposedupstream and downstream from the liquid discharge head unit 210C forcyan, respectively. Similarly, a first roller CR1M and a second rollerCR2M are disposed upstream and downstream from the liquid discharge headunit 210M, respectively. Similarly, a first roller CR1Y and a secondroller CR2Y are disposed upstream and downstream from the liquiddischarge head unit 210Y, respectively.

The liquid discharge apparatus 110 includes, for example, sensor devices(e.g., sensor devices SENK, SENC, SENM, and SENY, also collectively“first sensor devices SEN”) for the liquid discharge head units,respectively, as illustrated in FIG. 2. The term “sensor device” in thisspecification means a group of components including a sensor. The liquiddischarge apparatus 110 can further include another sensor device (i.e.,a second sensor device SEN2) upstream from the first sensor devices SENin the conveyance direction 10. That is, the second sensor device SEN2is the extreme upstream one of the sensor devices when the second sensordevice SEN2 is provided.

In the example illustrated in FIG. 2, the liquid discharge apparatus 110includes four first sensor devices SEN and one second sensor deviceSEN2, that is, five sensor devices in total.

In the description below, the first sensor devices SEN and the secondsensor device SEN2 may be collectively referred to as sensor devices,and the optical sensors (area sensors) of the first sensor devices andthe second sensor device may be referred to as first sensors and asecond sensor or collectively sensors. The structures and locations ofthe sensor devices are not limited to those illustrated in the drawings.

Although the number of the sensor devices is five in the descriptionbelow, the number of the sensor devices is not limited to five. Thenumber of the first and second sensor devices in total can be greaterthan the number of the liquid discharge head units as illustrated inFIG. 2. For example, each liquid discharge head unit 210 can be providedwith two or greater number of sensor devices. Similarly, two secondsensor devices SEN2 can be used. Alternatively, the second sensor deviceSEN2 can be omitted.

For example, the sensor device SEN includes an optical sensor OS(illustrated in FIG. 7) employing visible light, laser light, infrared,or the like. Note that the optical sensor OS can be is a charge-coupleddevice (CCD) camera or a complementary metal oxide semiconductor (CMOS)camera. That is, the sensor device SEN includes a sensor to detectsurface data of the web 120. The liquid discharge apparatus 110 detects,with the sensor device SEN, the surface data of the conveyed objectduring image formation and detects at least one of the relativeposition, speed of movement, and the amount of movement of the conveyedobject among a plurality of detection results. Note that the sensordevices can be of same type or different types. In the descriptionbelow, the sensor devices are of same type.

As described later, the sensor device includes a laser light source(hereinafter “light source LG”). As the laser light emitted from thelight source LG is diffused on the surface of the web 120 andsuperimposed diffusion waves interfere with each other, a pattern suchas a speckle pattern is generated. The optical sensor OS of the sensordevice SEN captures and images the pattern such as the speckle pattern.The speckle pattern is an example of surface data of the web 120. Basedon the change of position of the pattern captured by the optical sensorOS, the sensor device SEN can detect at least one of the relativeposition, speed of movement, and the amount of movement of the conveyedobject. Then, the liquid discharge apparatus 110 can obtain the amountby which the liquid discharge head unit 210 is to be moved, the timingof ink discharge from the liquid discharge head unit 210, or the like.

Further, the term “location of sensor device” means the positionregarding which the sensor device SEN performs detection (e.g., positiondetection), that is, the position to be detected by the sensor device.Accordingly, it is not necessary that all components relating to thedetection are disposed at the “location of sensor device”. In oneembodiment, only the optical sensor OS is disposed at the position wherethe sensor device SEN performs detection, and other components arecoupled to the optical sensor OS via a cable and disposed awaytherefrom. By contrast, in another embodiment, all components relatingto the detection are disposed at the “location of sensor device”. InFIG. 2, references “SENK, SENC, SENM, SENY, and SEN2” are given atrespective example locations of sensor devices in the liquid dischargeapparatus 110. In the description below, the sensor devices SENK, SENC,SENM, SENY, and SEN may be collectively referred to as “sensor devices”.

The optical sensor OS is preferably disposed close to the ink dischargeposition. That is, the distance between the ink discharge position andthe sensor device SEN is preferably short. When the distance between theink discharge position and the first sensor device SEN is short,detection error can be suppressed. Accordingly, the liquid dischargeapparatus 110 can accurately detect, with the first sensor device SEN,the position of the recording medium in the conveyance direction 10 orthe orthogonal direction 20.

Referring back to FIG. 2, in the description below, the sensor deviceSEN provided for the liquid discharge head unit 210K for black isreferred to as “sensor device SENK”. Similarly, the sensor device SENprovided for the liquid discharge head unit 210C for cyan is referred toas “sensor device SENC”. The sensor device provided for the liquiddischarge head unit 210M for magenta is referred to as “sensor deviceSENM”. The sensor device provided for the liquid discharge head unit210Y for yellow is referred to as “sensor device SENY”.

Specifically, the sensor device SEN is disposed between the first rollerCR1 and the second roller CR2. In the illustrative embodiment, thesensor device SENK for black is preferably disposed in an inter-rollerrange INTK1 between the first and second rollers CR1K and CR2K.Similarly, the sensor device SENC for cyan is preferably disposed in aninter-roller range INTC1 between the first and second rollers CR1C andCR2C. The sensor device SENM for magenta is preferably disposed in aninter-roller range INTM1 between the first and second rollers CR1M andCR2M. The sensor device SENY for yellow is preferably disposed in aninter-roller range INTY1 between the first and second rollers CR1Y andCR2Y. The inter-roller ranges INTY1, INTC1, INTM1, and INTY1 arecollectively referred to as “inter-roller ranges INT1”. The first sensordevice SEN disposed between the first and second rollers CR1 and CR2 candetect the recording medium at a position close to the ink dischargeposition. Further, since the moving speed is relatively stable in aportion between the rollers, the liquid discharge apparatus 110 candetect the position of the recording medium in the orthogonal direction20, with a high accuracy.

More preferably, in each inter-roller ranges INT1, the first sensordevice SEN is disposed between the ink discharge position and the firstroller CR1. In other words, the first sensor device SEN is preferablydisposed upstream from the ink discharge position in the conveyancedirection 10.

Specifically, the sensor device SENK for black is, more preferably,disposed in a range extending between the black ink discharge positionPK and the first roller CR1K for black (hereinafter “upstream rangeINTK2”). Similarly, the sensor device SENC for cyan is, more preferably,disposed in a range extending between the cyan ink discharge position PCand the first roller CR1C for cyan (hereinafter “upstream range INTC2”).The sensor device SENM for magenta is, more preferably, disposed in arange extending between the magenta ink discharge position PM and thefirst roller CR1M for magenta (hereinafter “upstream range INTM2”). Thesensor device SENY for yellow is, more preferably, disposed in a rangeextending between the yellow ink discharge position PY and the firstroller CR1Y for yellow (hereinafter “upstream range INTY2”).

When the first sensor devices SEN are respectively disposed in theupstream ranges INTK2, INTC2, INTM2, and INTY2, the liquid dischargeapparatus 110 can detect the position of the recording medium (conveyedobject) in the orthogonal direction 20, with a high accuracy. The firstsensor devices SEN thus disposed are upstream from the landing positionat which ink droplets land on the recording medium in the conveyancedirection 10. Accordingly, the liquid discharge apparatus 110 caninitially detect the position of the recording medium with the firstsensor device SEN high a high accuracy and then calculate the inkdischarge timing (i.e., operation timing) of each liquid discharge headunit 210, the amount by which each liquid discharge head unit 210 is tomove, or a combination thereof.

In other words, in a period from when the position of a given portion ofthe web 120 (conveyed object) is detected on the upstream side of theink landing position to when the detected portion of the web 120 reachesthe ink landing position, adjustment of the timing to discharge theliquid, moving of the liquid discharge head unit 210, or the combinationthereof can be performed. Accordingly, the liquid discharge head unit210 can accurately change the landing position in at least one of theconveyance direction 10 and the orthogonal direction 20.

Note that, if the first sensor device SEN is disposed directly below theliquid discharge head unit 210, in some cases, a delay of control actioncauses misalignment in color superimposition (out of color registration)resulting in color shift. Accordingly, when the location of sensordevice is upstream from the ink landing position, misalignment in colorsuperimposition is suppressed, improving image quality. There are caseswhere layout constraints hinder disposing the first sensor device SENadjacent to the landing position. Accordingly, the first sensor deviceSEN is preferably disposed closer to the first roller CR1 from the inklanding position.

The location of sensor device can be directly below the liquid dischargehead unit 210. The sensor device SEN disposed directly below the headunit can accurately detect the amount of movement of the recordingmedium directly below the head unit. Therefore, in a configuration inwhich the speed of control action is relatively fast, the sensor deviceis preferably disposed closer to the position directly below the liquiddischarge head unit 210. However, the location of sensor device is notlimited to a position directly below the liquid discharge head unit 210,and similar calculation is feasible when the sensor device is disposedotherwise.

Alternatively, in a configuration in which error is tolerable, thesensor device can be disposed directly below the liquid discharge headunit, or between the first and second rollers and downstream from theposition directly below the liquid discharge head unit.

In an arrangement in which the first sensor devices SEN are evenlyspaced, the second sensor device SEN2 is preferably spaced similarly.The description below is based on the arrangement illustrated in FIG. 2.Specifically, there are cases where the first sensor devices SEN areevenly spaced. That is, a distance between the sensor device SENK andthe sensor device SENC, a distance between the sensor device SENC andthe sensor device SENM, and a distance between the sensor device SENMand the sensor device SENY are similar. In this arrangement, the secondsensor device SEN2 is preferably disposed so that a distance between thesecond sensor device SEN2 and the sensor device SENK is similar to adistance between the sensor device SENK and the sensor device SENC. Theaccuracy of detection by the sensor devices is generally calculatedbased on the distance between the sensor devices. Accordingly, disposingthe sensor devices at equal distances is advantageous in equalizing theaccuracy of detection.

Additionally, the location of the second sensor device is preferablydownstream from a roller around which the conveyed object twines. Forexample, if the web 120 twines or winds around the roller, the positionof the web 120 easily changes. Accordingly, it is preferable to detectthe web 120 with the second sensor device after such twining occurs,that is, downstream from the position where such twining occurs. Thisplacement can reduce the adverse effect of the twining with thedetection result of the second sensor device. Note that, in the exampleillustrated in FIG. 2, the web 120 may twine the roller 230. If the web120 is looped around a roller at a relatively sharp angle asillustrated, the web 120 may twine the roller and fluctuate in position.Accordingly, in the example illustrated in FIG. 2, the second sensordevice SEN2 is preferably disposed downstream from the roller 230.

FIG. 3 is a schematic plan view illustrating an arrangement of thesensor devices SEN and the actuators AC of the liquid dischargeapparatus illustrated in FIG. 3. Referring to FIG. 2, when viewed in thedirection vertical to the recording surface of the web 120, for example,the sensor device SEN is preferably disposed at a position close to anend of the web 120 in the width direction (the orthogonal direction 20)of the web 120 and overlapping with the web 120. The sensor devices SENare disposed at positions PS1, PS2, PS3, PS4, and PS20 in FIG. 3,respectively. In the configuration illustrated in FIGS. 2 and 3, thecontroller 520 can control the actuators AC1, AC2, AC3, and AC4 to movethe liquid discharge head units 210Y, 210M, 210C, and 210K,respectively, in both the conveyance direction 10 in which the web 120is conveyed and the orthogonal direction 20 orthogonal thereto.

In the configuration illustrated in FIG. 2, the sensor devices SEN aredisposed facing a back side (lower side in FIG. 2) of the web 120opposite the liquid discharge head units 210.

To the actuators AC1, AC2, AC3, and AC4, actuator controllers CTL1,CTL2, CTL3, and CTL4 are connected to control the actuators AC1, AC2,AC3, and AC4, respectively.

The actuator ACT is, for example, a linear actuator or a motor. Theactuator can include a control circuit, a power circuit, and amechanical component.

For example, the actuator controller CTL1, CTL2, CTL3, and CTL4(hereinafter collectively “actuator controllers CTL”) include drivercircuits.

FIG. 4 is a block diagram of a hardware configuration to calculatedisplacement of the conveyed object, according to the presentembodiment. In the illustrated example, the liquid discharge apparatus110 includes a plurality of actuators and a plurality of sensor devices.In the illustrated example, the controller 520 is mounted in the liquiddischarge apparatus 110. The controller 520 includes a centralprocessing unit (CPU) 221, a read only memory (ROM) 222, and a randomaccess memory (RAM) 223. As illustrated in the drawing, each device,such as the first sensor devices SENK, SENC, SENM, and SENY (alsocollectively “first sensor devices SEN1”), the second sensor deviceSEN2, and the actuators AC1, AC2, AC3, and AC4, can further include aninput/output (I/O) interface for data transmission and reception withanother device.

Note that the configuration is not limited to the illustratedconfiguration. That is, the illustrated devices can be components ofeither the liquid discharge apparatus 110 or an external apparatus.

Some of the illustrated components may be shared by two or more devices.For example, the CPU 221 can double as a CPU to implement a detectingunit to be described later.

The CPU 221 is examples of the processor and the controller.Specifically, the CPU 221 acquires detection results generated by thesensors and performs operation to calculate the displacement of theconveyed object. Further, the CPU 221 controls the actuators AC to movethe liquid discharge head units 210.

The ROM 222 and the RAM 223 are examples of memories. For example, theROM 222 stores programs and data used by the CPU 221. Additionally, theRAM 223 stores the program for the operation performed by the CPU 221and serves as a memory region to implement the operation.

A speed detection circuit SCR is an electronic circuit to detect, forexample, the speed at which the conveyed object is conveyed. Note thatthe speed detection circuit SCR can be either identical to or differentfrom the processor such as the CPU 221.

FIGS. 5A and 5B are schematic views illustrating external shapes of theliquid discharge head unit according to the present embodiment. FIG. 5Ais a schematic plane view of one of the four liquid discharge head units210K to 210Y of the liquid discharge apparatus 110.

In the example illustrated in FIG. 5A, the liquid discharge head unit210 is a line head unit. That is, the liquid discharge apparatus 110includes the four liquid discharge head units 210K, 210C, 210M, and 210Yarranged in the order of black, cyan, magenta, and yellow in theconveyance direction 10.

In this example, the liquid discharge head unit 210K includes four heads210K-1, 210K-2, 210K-3, and 210K-4 arranged in a staggered manner in theorthogonal direction 20. With this arrangement, the liquid dischargeapparatus 110 can form an image throughout the image formation area onthe web 120 in the width direction orthogonal to the conveyancedirection 10. The liquid discharge head units 210C, 210M, and 210Y aresimilar in structure to the liquid discharge head unit 210K, and thedescriptions thereof are omitted to avoid redundancy.

Although the description above concerns a liquid discharge head unitincluding four heads, a liquid discharge head unit including a singlehead can be used.

Conveyed Object Detector

FIG. 6 is a schematic block diagram illustrating a hardwareconfiguration to implement a conveyed object detector 600 of the liquiddischarge apparatus 110, to detect the conveyed object. For example, theconveyed object detector 600 is implemented by hardware such as thesensor devices SEN and the controller 520, illustrated in the drawing.

The sensor device SEN is described below.

FIG. 7 is an external view of the sensor device SEN included in theconveyed object detector 600.

The conveyed object detector 600 illustrated in the drawing isconfigured to irradiated a conveyed object, such as a recording medium(e.g., a web), with light to form a speckle pattern. Specifically, thesensor device SEN includes the light source LG including a plurality oflight-emitting parts. To obtain an image of the speckle pattern, thesensor device SEN further includes the optical sensor OS (e.g., a CMOSimage sensor) and a telecentric optics (TO) to condense light to imagethe speckle pattern on the CMOS image sensor.

For example, the optical sensor OS performs imaging of the specklepattern. Then, the controller 520 performs processing such ascorrelation operation based on the image obtained by one optical sensorOS and the image obtained by the optical sensor OS of another sensordevice SEN. In this case, the controller 520 calculates, for example,the amount of movement of the conveyed object from one optical sensor OSto the other optical sensor OS. Alternatively, the same optical sensorOS can capture an image of the pattern at a time T1 and an image of thepattern at a time T2. Then, correlation operation can be made using theimage of the pattern obtained at the time T1 (time point) and the imageof the pattern obtained at the time T2 (time point). In this case, thecontroller 520 outputs the amount of movement from the time T1 to thetime T2. Thus, the image obtained at times T1 and T2 serve as thesurface data detected at least two different time points. In theillustrated example, the sensor device SEN has a width W of 15 mm, adepth D of 60 mm, and a height H of 32 mm (15×60×32).

The light source is not limited to devices employing laser light but canbe, for example, a light emitting diode (LED) or an organic electroluminescence (EL). Depending on the type of light source, the pattern tobe detected is not limited to the speckle pattern. Descriptions aregiven below of an example in which the pattern is a speckle pattern.

The CMOS image sensor is an example hardware structure to implement animaging unit 16 (16A or 16B) to be described later. Although thecontroller 520 performs the correlation operation in this example, inone embodiment, a field-programmable gate array (FPGA) circuit of one ofthe sensor devices SEN performs the correlation operation.

A control circuit 152 controls the optical sensor OS, the light sourceLG, and the like disposed inside the sensor device SEN. Specifically,the control circuit 152 outputs trigger signals to a detection circuit50 to control the shutter timing of the optical sensor OS. The controlcircuit 152 controls the optical sensor OS to acquire thetwo-dimensional image data therefrom. Then, the control circuit 152transmits the two-dimensional image data generated by the optical sensorOS to the memory device 53. The control circuit 152 further outputs asignal to designate an irradiated area, to the light source LG. Inanother embodiment, the control circuit 152 is implemented by the FPGAcircuit, for example.

The memory device 53 is a so-called memory. The memory device 53preferably has a capability to divide the two-dimensional image datatransmitted from the control circuit 152 and store the divided imagedata in different memory ranges.

The controller 520 performs operations using the image data stored inthe memory device 53.

The control circuit 152 and the controller 520 are, for example, centralprocessing units (CPUs) or electronic circuits. Note that the controlcircuit 152, the memory device 53, and the controller 520 are notnecessarily different devices. For example, the control circuit 152 andthe controller 520 can be implemented by a single CPU.

FIG. 8A is a functional block diagram of the conveyed object detector600. Although the sensor devices SEN are respectively provided for theliquid discharge head units 210, in the example described below, adetecting unit 110F10 is implemented by a combination of sensor devicesSENK and SENC for the liquid discharge head units 210K and 210C and theconveyed object detector 600 including the controller 520, asillustrated in FIG. 8A. In this example, an image obtaining unit 52A,which is the function of the sensor device SENK to obtain an image,outputs data of imaging at a position A, and an image obtaining unit52B, which is the function of the sensor device SENC to obtain an image,outputs data of imaging at a position B.

The image obtaining unit 52A for the liquid discharge head unit 210Kincludes, for example, an imaging unit 16A, an imaging controller 14A,an image memory 15A, and a light source unit 51A, and a light sourcecontroller 56A. In this example, the image obtaining unit 52B for theliquid discharge head unit 210C is similar in configuration to the imageobtaining unit 52A. The image obtaining unit 52B includes an imagingunit 16B, an imaging controller 14B, and an image memory 15B. The imageobtaining unit 52A is described below, and redundant descriptions areomitted.

The imaging unit 16A captures an image of the web 120 conveyed in theconveyance direction 10. The imaging unit 16A is implemented by, forexample, the optical sensor OS (illustrated in FIG. 7). The imaging unit16A includes a setting unit 58A to set the detection area of the sensordevice SEN.

The configuration illustrated in FIG. 8B is different from theconfiguration illustrated in FIG. 8A only in that the setting units 58Aand 58B (hereinafter collectively “setting units 58”) are mounted in theimaging controllers 14A and 14B, respectively.

The imaging controller 14A includes a shutter controller 141A and animage acquisition unit 142A. The imaging controller 14A is implementedby, for example, the control circuit 152.

The image acquisition unit 142A acquires the image data generated by theimaging unit 16A.

The shutter controller 141A controls the timing of imaging by theimaging unit 16A.

The image memory 15A stores the image data acquired by the imagingcontroller 14A. The image memory 15A is implemented by, for example, thememory device 53 and the like (illustrated in FIG. 6).

The light source unit 51A irradiates the web with light such as laserlight. The light source unit 51A is implemented by, for example, thelight source LG (illustrated in FIG. 7).

The light source controller 56A controls turning on and off and theamount of light of a plurality of light-emitting elements of the lightsource unit 51A. The light source controller 56A is implemented by, forexample, the control circuit 152.

The light source controller 56A is controlled by an adjusting unit 55F.As described later, the adjusting unit 55F controls the light sourcecontroller 56A to change the area irradiated by the light source unit51A (i.e., the irradiated area). The adjusting unit 55F is implementedby, for example, the controller 520.

A calculator 53F is configured to calculate, based on the image datarecorded in the image memories 15A and 15B, the position of the patternon the web 120, the speed at which the web 120 moves (hereinafter“moving speed”), and the amount of movement of the web 120.Additionally, the calculator 53F outputs, to the shutter controllers141A and 141B, data on time difference Δt indicating the timing ofshooting (shutter timing). In other words, the calculator 53F caninstruct the shutter controller 141A of shutter timings of imaging atthe position A and imaging at the position B with the time differenceΔt. The calculator 53F is implemented by, for example, the controller520 or a processor.

The web 120 has diffusiveness on a surface thereof or in an interiorthereof. Accordingly, when the web 120 is irradiated with light (e.g.,laser beam) of the light source unit 51A or 51B, the reflected light isdiffused. The diffuse reflection creates a pattern on the web 120. Thepattern is made of spots called “speckles” (i.e., a speckle pattern).Accordingly, when the web 120 is shot, an image of the speckle patternis obtained. From the image, the position of the speckle pattern isknown, and a relative position of a specific portion of the web 120 canbe detected. The speckle pattern is generated as the light emitted tothe web 120 interferes with a rugged shape caused by a projection and arecess, on the surface or inside of the web 120.

As the web 120 is conveyed, the speckle pattern on the web 120 isconveyed as well. When an identical speckle pattern is detected atdifferent time points, the calculator 53F obtains the amount of movementof the web 120 based on the detection result. In other words, thecalculator 53F obtains the amount of movement of the speckle patternbased on multiple number of times of detection of an identical specklepattern, thereby obtaining the amount of movement of the web 120.Further, the calculator 53F converts the calculated amount of movementinto an amount of movement per unit time, thereby obtain the speed atwhich the web 120 has moved.

As illustrated in FIG. 8A, the imaging unit 16A and the imaging unit 16Bare disposed at a regular interval (given reference “L” in FIG. 8A) fromeach other in the conveyance direction 10. Via the imaging units 16A and16B, images of the web 120 are taken at the respective positions.

The shutter controllers 141A and 141B cause the imaging units 16A and16B to perform imaging of the web 120 at an interval of time differenceΔt. Then, based on the pattern represented by the image data generatedby the imaging, the calculator 53F obtains the amount of movement of theweb 120. The time difference Δt can be expressed by Formula 1 below,where V represents a conveyance speed (mm/s) in an ideal conditionwithout displacement, and L represents a relative distance, which is thedistance (mm) between the imaging unit 16A and the imaging unit 16B inthe conveyance direction 10.Δt=L/V  Formula 1

In Formula 1 above, the relative distance L (mm) between the imagingunit 16A and the imaging unit 16A and is obtained preliminarily.

The calculator 53F performs cross-correlation operation of image dataD1(n) generated by the image obtaining unit 52A and image data D2(n)generated by the image obtaining unit 52B. Hereinafter image datagenerated by the cross-correlation operation is referred to as“correlated image data”. For example, based on the correlated imagedata, the calculator 53F calculates the displacement amount ΔD(n), whichis the amount of displacement from the position detected with theprevious frame or by another sensor device. For example, thecross-correlation operation is expressed by Formula 2 below.D1*D2*=F−1[F[D1]·F[D2]*]  Formula 2

Note that, the image data D1(n) in Formula 2, that is, the data of theimage taken at the position A, is referred to as the image data D1.Similarly, the image data D2(n) in Formula 2, that is, the data of theimage taken at the position B, is referred to as the image data D2. InFormula 2, “F[ ]” represents Fourier transform, “F−1[ ]” representsinverse Fourier transform,

“*” represents complex conjugate, and “*” represents cross-correlationoperation.

As represented in Formula 2, image data representing the correlationimage is obtained through cross-correlation operation “D1*D2” performedon the first image data D1 and the second image data D2. Note that, whenthe first image data D1 and the second image data D2 are two-dimensionalimage data, the correlated image data is two-dimensional image data.When the first image data D1 and the second image data D2 areone-dimensional image data, the image data representing the correlationimage is one-dimensional image data.

Regarding the correlation image, when a broad luminance profile causesan inconvenience, phase only correlation can be used. For example, phaseonly correlation is expressed by Formula 3 below.D1*D2*=F−1[P[F[D1]]·P[F[D2]*]]  Formula 3

In Formula 3, “P[ ]” represents taking only phase out of complexamplitude, and the amplitude is considered to be “1”.

Thus, the calculator 53F can obtain the displacement amount ΔD(n) basedon the correlation image even when the luminance profile is relativelybroad.

The correlation image represents the correlation between the first imagedata D1 and the second image data D2. Specifically, as the match ratebetween the first image data D1 and the second image data D2 increases,a luminance causing a sharp peak (so-called correlation peak) is outputat a position close to a center of the correlated image data. When thefirst image data D1 matches the second image data D2, the center of thecorrelation image and the peak position overlap.

Based on the correlation operation, the calculator 53F outputs thedisplacement in position, the amount of movement, or the speed ofmovement between the first image data D1 and the second image data D2obtained at the time difference Δt. For example, the conveyed objectdetector 600 detects the amount by which the web 120 has moved in theorthogonal direction 20 from the position of the first image data D1 tothe position of the second image data D2. Alternatively, the result ofcorrelation operation can be the speed of movement instead of the amountof movement. Thus, the calculator 53F can calculate the amount ofmovement of the liquid discharge head unit 210C for cyan based on theresult of the correlation operation.

Based on the calculation result generated by the calculator 53F, a headmoving unit 57F controls the actuator AC2 illustrated in FIG. 3, therebycontrolling the landing position of the liquid. The head moving unit 57Fis implemented by, for example, the actuator controller CTL.Alternatively, the head moving unit 57F can be implemented by acombination of the actuator controller CTL and the controller 520. Yetalternatively, the head moving unit 57F can be implemented by thecontroller 520.

Further, based on the result of correlation operation, the calculator53F can obtain the difference between the conveyance amount of the web120 in the conveyance direction 10 and the relative distance L. That is,the calculator 53F can be also used to calculate the positions of theweb 120 in both of the conveyance direction 10 and the orthogonaldirection 20, based on the two-dimensional (2D) image data generated bythe imaging units 16A and 16B. Sharing the sensor device in detectingpositions in both directions can reduce the cost of the sensor devices.Additionally, the space for the detection can be small since the numberof sensor devices is reduced.

Based on the calculated difference of the conveyance amount of the web120 from an ideal distance, the calculator 53F calculates the timing ofink discharge from the liquid discharge head unit 210C for cyan. Basedon the calculation result, a discharge controller 54F controls inkdischarge from the liquid discharge head unit 210C for cyan. Thedischarge controller 54F outputs a second signal SIG2 to control thetiming of ink discharge from the liquid discharge head unit 210C. Whenthe timing of ink discharge from the liquid discharge head unit 210K iscalculated, the discharge controller 54F outputs a first signal SIG1 tocontrol the ink discharge from the liquid discharge head unit 210K. Thedischarge controller 54F is implemented by, for example, the controller520 (illustrated in FIG. 2).

The liquid discharge apparatus according to the present embodiment canfurther includes a gauge such as an encoder. Descriptions are givenbelow of a configuration including an encoder 300 serving as the gauge.For example, the encoder 300 is attached to a rotation shaft of theroller 230, which is a driving roller. Then, the encoder 300 can measurethe amount of movement of the web 120 in the conveyance direction 10,based on the amount of rotation of the roller 230. When the measurementresults are used in combination with the detection results generated bythe sensor device SEN, the liquid discharge apparatus 110 can dischargeliquid onto the web 120 more accurately.

For example, the correlation operation is performed as follows.

Example of Correlation Operation

FIG. 9 is a diagram of a configuration for the correlation operationaccording to the present embodiment. For example, the calculator 53Fperforms the correlation operation with the illustrated configuration,to calculate the relative position of the web 120 in the orthogonaldirection at the position where the image data is obtained, the amountof movement, speed of movement, or a combination thereof. Alternatively,with the correlation operation, the amount of displacement of the web120 from the ideal position at the timing when the image data isobtained or the speed of displacement can be calculated.

Specifically, the calculator 53F includes a 2D Fourier transform FT1 (afirst 2D Fourier transform), a 2D Fourier transform FT2 (second 2DFourier transform), a correlation image data generator DMK, a peakposition search unit SR, an arithmetic unit CAL (or arithmetic logicalunit), and a transform-result memory MEM.

The 2D Fourier transform FT1 is configured to transform the first imagedata D1. The 2D Fourier transform FT1 includes a Fourier transform unitFT1 a for transform in the orthogonal direction 20 and a Fouriertransform unit FT1 b for transform in the conveyance direction 10.

The Fourier transform unit FT1 a performs one-dimensional transform ofthe first image data D1 in the orthogonal direction 20. Based on theresult of transform by the Fourier transform unit FT1 a for orthogonaldirection, the Fourier transform unit FT1 b performs one-dimensionaltransform of the first image data D1 in the conveyance direction 10.Thus, the Fourier transform unit FT1 a and the Fourier transform unitFT1 b perform one-dimensional transform in the orthogonal direction 20and the conveyance direction 10, respectively. The 2D Fourier transformFT1 outputs the result of transform to the correlation image datagenerator DMK.

Similarly, the 2D Fourier transform FT2 is configured to transform thesecond image data D2. The 2D Fourier transform FT2 includes a Fouriertransform unit FT2 a for transform in the orthogonal direction 20, aFourier transform unit FT2 b for transform in the conveyance direction10, and a complex conjugate unit FT2 c.

The Fourier transform unit FT2 a performs one-dimensional transform ofthe second image data D2 in the orthogonal direction 20. Based on theresult of transform by the Fourier transform unit FT2 a for orthogonaldirection, the Fourier transform unit FT2 b performs one-dimensionaltransform of the second image data D2 in the conveyance direction 10.Thus, the Fourier transform unit FT2 a and the Fourier transform unitFT2 b perform one-dimensional transform in the orthogonal direction 20and the conveyance direction 10, respectively.

Subsequently, the complex conjugate unit FT2 c calculates a complexconjugate of the results of transform by the Fourier transform unit FT2a (for orthogonal direction) and the Fourier transform unit FT2 b (forconveyance direction). Then, the 2D Fourier transform FT2 outputs, tothe correlation image data generator DMK, the complex conjugatecalculated by the complex conjugate unit FT2 c.

The correlation image data generator DMK then generates the correlationimage data, based on the transform result of the first image data D1,output from the 2D Fourier transform FT1, and the transform result ofthe second image data D2, output from the 2D Fourier transform FT2.

The correlation image data generator DMK includes an adder DMKa and a 2Dinverse Fourier transform unit DMKb.

The adder DMKa adds the transform result of the first image data D1 tothat of the second image data D2 and outputs the result of addition tothe 2D inverse Fourier transform unit DMKb.

The 2D inverse Fourier transform unit DMKb performs 2D inverse Fouriertransform of the result generated by the adder DMKa. Thus, thecorrelation image data is generated through 2D inverse Fouriertransform. The 2D inverse Fourier transform unit DMKb outputs thecorrelation image data to the peak position search unit SR.

The peak position search unit SR searches the correlation image data fora peak position (a peak luminance or peak value), at which rising issharpest. To the correlation image data, values indicating the intensityof light, that is, the degree of luminance, are input. The luminancevalues are input in matrix.

Note that, in the correlation image data, the luminance values arearranged at a pixel pitch of the optical sensor OS (i.e., an areasensor), that is, pixel size intervals. Accordingly, the peak positionis preferably searched for after performing so-called sub-pixelprocessing. Sub-pixel processing enhances the accuracy in searching forthe peak position. Then, the calculator 53F can output the position, theamount of movement, and the speed of movement.

An example of searching by the peak position search unit SR is describedbelow.

FIG. 10 is a graph illustrating the peak position searched in thecorrelation operation according to the present embodiment. In thisgraph, the lateral axis represents the position in the conveyancedirection 10 of an image represented by the correlation image data, andthe vertical axis represents the luminance values of the imagerepresented by the correlation image data.

The luminance values indicated by the correlation image data aredescribed below using a first data value q1, a second data value q2, anda third data value q3. In this example, the peak position search unit SR(illustrated in FIG. 9) searches for peak position P on a curved line kconnecting the first, second, and third data values q1, q2, and q3.

Initially, the peak position search unit SR calculates each differencebetween the luminance values indicated by the correlation image data.Then, the peak position search unit SR extracts a largest differencecombination, meaning a combination of luminance values between which thedifference is largest among the calculated differences. Then, the peakposition search unit SR extracts combinations of luminance valuesadjacent to the largest difference combination. Thus, the peak positionsearch unit SR can extract three data values, such as the first, second,and third data values q1, q2, and q3 in the graph. The peak positionsearch unit SR calculates the curved line K connecting these three datavalues, thereby obtaining the peak position P. In this manner, the peakposition search unit SR can reduce the amount of operation such assub-pixel processing to increase the speed of searching for the peakposition P. The position of the combination of luminance values betweenwhich the difference is largest means the position at which rising issharpest. The manner of sub-pixel processing is not limited to thedescription above.

Through the searching of the peak position P performed by the peakposition search unit SR, for example, the following result is attained.

FIG. 11 is a diagram of example results of correlation operation andillustrates a profile of strength of correlation of a correlationfunction. In this drawing, X axis and Y axis represent serial number ofpixel. The peak position search unit SR (illustrated in FIG. 9) searchesfor a peak position such as “correlation peak” in the graph.

Referring back to FIG. 9, the arithmetic unit CAL calculates therelative position, amount of movement, or speed of movement of the web120, or a combination thereof. For example, the arithmetic unit CALcalculates the difference between a center position of the correlationimage data and the peak position calculated by the peak position searchunit SR, to obtain the relative position and the amount of movement.

For example, the arithmetic unit CAL divides the amount of movement bytime, to obtain the speed of movement.

Thus, the calculator 53F can calculate, through the correlationoperation, the relative position, amount of movement, or speed ofmovement of the web 120. The methods of calculation of the relativeposition, the amount of movement, or the speed of movement are notlimited to those described above. For example, alternatively, thecalculator 53F obtains the relative position, amount of movement, orspeed of movement through the following method.

Initially, the calculator 53F binarizes each luminance value of thefirst image data D1 and the second image data D2. That is, thecalculator 53F binarizes a luminance value not greater than apredetermined threshold into “0” and a luminance value grater than thethreshold into “1”. Then, the calculator 53F may compare the binarizedfirst and second image data D1 and D2 to obtain the relative position.

Although the description above concerns a case where fluctuations arepresent in Y direction, the peak position occurs at a position displacedin the X direction when there are fluctuations in the X direction.

Alternatively, the calculator 53F can adapt a different method to obtainthe relative position, amount of movement, or speed of movement. Forexample, the calculator 53F can adapt so-called pattern matchingprocessing to detect the relative position based on a pattern taken inthe image data.

Example of Occurrence of Displacement

Descriptions are given below of displacement of the recording medium inthe orthogonal direction 20, with reference to FIGS. 12A and 12B, whichare plan views of the web 120 being conveyed. In FIG. 12A, the web 120is conveyed in the conveyance direction 10. While the web 120 isconveyed by the rollers (such as the rollers 230, CR1, and CR2 in FIG.2), the position of the web 120 may fluctuate in the orthogonaldirection 20 as illustrated in FIG. 12B. That is, the web 120 maymeander as illustrated in FIG. 12B.

Note that, the roller is disposed oblique to the conveyance direction 10in the illustrated example. In the drawing, the obliqueness isexaggerated, and the degree of obliqueness may be smaller than thedegree illustrated.

The fluctuation of the position of the web 120 in the orthogonaldirection 20 (hereinafter “orthogonal position of the web 120”), thatis, the meandering of the web 120, is caused by eccentricity of aconveyance roller (the driving roller in particular), misalignment, ortearing of the web 120 by a blade. When the web 120 is relatively narrowin the orthogonal direction 20, for example, thermal expansion of theroller affect fluctuation of the web 120 in the orthogonal position.

For example, when vibration is caused by eccentricity of the roller orcutting with a blade, the web 120 can meander as illustrated.Additionally, when the cutting with the blade is uneven, meandering canbe also caused by a physical property of the web 120, that is, the shapeof the web 120 after the cutting.

Descriptions are given below of a cause of misalignment in colorsuperimposition (out of color registration) with reference to FIG. 13.Due to fluctuations (meandering illustrated in FIG. 12B) of the web 120(the recording medium) in the orthogonal direction 20, misalignment incolor superimposition is likely to occur as illustrated in FIG. 13.

Specifically, to form a multicolor image on the recording medium using aplurality of colors, the liquid discharge apparatus 110 superimposes aplurality of different color inks discharged from the liquid dischargehead units 210, through so-called color plane, on the web 120.

As illustrated in FIG. 12B, the web 120 can fluctuate in position andmeanders, for example, with reference to lines 320. Assuming that theliquid discharge head units 210 discharge respective inks to anidentical portion (i.e., an intended droplet landing position) on theweb 120 in this state, a portion 330 out of color registration iscreated since the intended droplet landing position fluctuates in theorthogonal direction 20 while the web 120 meanders between the liquiddischarge head units 210. The portion 330 out of color registration iscreased as the position of a line or the like, drawn by the respectiveinks discharged from the liquid discharge head units 210, shakes in theorthogonal direction 20. The portion 330 out of color registrationdegrades the quality of the image on the web 120.

[Controller]

The controller 520 is described below.

FIG. 14 is a schematic block diagram of control configuration accordingto the present embodiment. For example, the controller 520 includes ahost 71 (or a higher-order device), such as an information processingapparatus, and an apparatus-side controller 72. In the illustratedexample, the controller 520 causes the apparatus-side controller 72 toform an image on a recording medium according to image data and controldata input from the host 71.

Examples of the host 71 include a client computer (personal computer orPC) and a server. The apparatus-side controller 72 includes a printercontroller 72C and a printer engine 72E.

The printer controller 72C governs operation of the printer engine 72E.The printer controller 72C transmits and receives the control data toand from the host 71 via a control line 70LC. The printer controller 72Cfurther transmits and receives the control data to and from the printerengine 72E via a control line 72LC. Through such data transmission andreception, the control data indicating printing conditions and the likeare input to the printer controller 72C. The printer controller 72Cstores the printing conditions, for example, in a resistor. The printercontroller 72C then controls the printer engine 72E according to thecontrol data to form an image based on print job data, that is, thecontrol data.

The printer controller 72C includes a central processing unit (CPU)72Cp, a print control device 72Cc, and a memory 72Cm. The CPU 72Cp andthe print control device 72Cc are connected to each other via a bus 72Cbto communicate with each other. The bus 72Cb is connected to the controlline 70LC via a communication interface (I/F) or the like.

The CPU 72Cp controls the entire apparatus-side controller 72 based on acontrol program and the like. That is, the CPU 72Cp is a processor aswell as a controller.

The print control device 72Cc transmits and receives data indicating acommand or status to and from the printer engine 72E, based on thecontrol date transmitted from the host 71. Thus, the print controldevice 72Cc controls the printer engine 72E.

To the printer engine 72E, a plurality of data lines, namely, data linesTOLD-C, TOLD-M, TOLD-Y, and TOLD-K are connected. The printer engine 72Ereceives the image data from the host 71 via the plurality of datalines. Then, the printer engine 72E performs image formation ofrespective colors, controlled by the printer controller 72C.

The printer engine 72E includes a plurality of data management devices,namely, data management devices 72EC, 72EM, 72EY, and 72EK. The printerengine 72E includes an image output 72Ei and a conveyance controller72Ec.

FIG. 15 is a block diagram of a configuration of the data managementdevice 72EC. For example, the plurality of data management devices 72EC,72EM, 72EY, and 72EK can have an identical configuration, and the datamanagement device 72EC is described below as a representative. Redundantdescriptions are omitted.

The data management device 72EC includes a logic circuit 72EC1 and amemory 72ECm. As illustrated in FIG. 15, the logic circuit 72EC1 isconnected via a data line 70LD-C to the host 71. The logic circuit 72EC1is connected via the control line 72LC to the print control device 72Cc.The logic circuit 72EC1 is implemented by, for example, an applicationspecific integrated circuit (ASIC) or a programmable logic device (PLD).

According to a control signal input from the printer controller 72C(illustrated in FIG. 14), the logic circuit 72EC1 stores, in the memory72ECm, the image data input from the host 71.

According to a control signal input from the printer controller 72C, thelogic circuit 72EC1 retrieves, from the memory 72ECm, cyan image dataIc. The logic circuit 72EC1 then transmits the cyan image data Ic to theimage output 72Ei. Similarly, magenta image data Im, yellow image dataIy, and black image data Ik are transmitted to the image output 72Ei.

The memory 72ECm preferably has a capacity to store image data extendingabout three pages. With the capacity to store image data extending aboutthree pages, the memory 72ECm can store the image data input from thehost 71, data image being used current image formation, and image datafor subsequent image formation.

FIG. 16 is a block diagram of a configuration of the image output 72Ei.In this block diagram, the image output 72Ei is constructed of an outputcontrol device 72Eic and the liquid discharge head units 210K, 210C,210M, and 210Y.

The output control device 72Eic outputs the image data for respectivecolors to the liquid discharge head units 210. That is, the outputcontrol device 72Eic controls the liquid discharge head units 210 basedon the image data input thereto.

The output control device 72Eic controls the plurality of liquiddischarge head units 210 either simultaneously or individually. That is,the output control device 72Eic receives timing commands and changes thetimings at which the liquid discharge head units 210 dischargerespective color inks. The output control device 72Eic can control oneor more of the liquid discharge head units 210 based on the controlsignal input from the printer controller 72C (illustrated in FIG. 14).Alternatively, the output control device 72Eic can control one or moreof the liquid discharge head units 210 based on user instructions.

In the example illustrated in FIG. 14, the apparatus-side controller 72has different routes for inputting the image data from the host 71 andfor transmission and reception of control data, with the host 71 and theapparatus-side controller 72.

The apparatus-side controller 72 may instruct formation of single-colorimages using one color ink, for example, black ink. In the case ofsingle-color image formation using black ink, to accelerate imageformation speed, the liquid discharge apparatus 110 can include one datamanagement device 72EK and four black liquid discharge head units 210K.In such as configuration, the plurality of black liquid discharge headunits 210K discharge black ink. Accordingly, the image formation speedis faster than that in the configuration using one black liquiddischarge head unit 210K.

The conveyance controller 72Ec (in FIG. 14) includes a motor and thelike. For example, the conveyance controller 72Ec controls the motorcoupled to the rollers to convey the web 120.

Example of setting of detection area for controlling liquid dischargeposition

FIG. 17 is a flowchart of operation performed by the liquid dischargeapparatus 110 according to the present embodiment. The setting unit 58illustrated in FIGS. 8A and 8B sets the detection area of the sensordevice SEN in detecting the conveyed object, for controlling the liquiddischarge position.

At S01, the liquid discharge apparatus 110 sets a counter value N to 1(N=1), where the counter value N represents the number of times ofprocessing including detection area setting and irradiated area setting.The counter value N being “1” is an example of an initial value. In thedescription below, the processing performed with the counter value Nbeing “1” is referred to as first time processing, and the processing isperformed three times (N=3).

At S02, the liquid discharge apparatus 110 determines whether thecounter value N is “1” (N=1). When the counter value N is “1” (Yes atS02), the process proceeds to Step S03. When the counter value N is not“1”, that is, the processing is not the first time (No at S02), theprocess proceeds to Step S09.

At S03, the liquid discharge apparatus 110 sets a first detection areaas initial setting of the detection area, for example, as illustrated inFIG. 18.

The initial setting is performed at S03 in FIG. 17, that is, before animage is formed on the web 120 according to image data.

In the illustrated example, the web 120 moves parallel to the conveyancedirection 10 without skew and meandering and does not move in theorthogonal direction 20. That is, the illustrated state is free of thefluctuations illustrated in FIG. 12B.

In the liquid discharge apparatus 110 illustrated in FIG. 2, the firstsensor devices SENK, SENC, SENM, and SENY perform the detection of theweb 120. The area in which the conveyed object detector 600 performs thedetection (i.e., the detection area) is, for example, a range in theimage data in which the calculator 53F performs calculation. Thedetection area can be the range of the image data output from theimaging unit 16A. Alternatively, in a configuration in which thecalculator 53F performs calculation in an area smaller than the entirearea of the image data, the detection area is the area in whichcalculation is performed.

The liquid discharge apparatus 110 is configured to set the detectionarea, specifically, position, size, or both of the detection area inwhich the conveyed object detector 600 performs the detection. In thedescription below, the term “first detection area” represents theposition, size, or both of the detection area set in the initial settingat S03.

Hereinafter, the term “first detection area SRK1” represents the area ofcalculation regarding the image data obtained by the sensor device SENKfor black. Similarly, the term “first detection area SRC1” representsthe area of calculation regarding the image data obtained by the sensordevice SENC for cyan. The terms “first detection area SRM1” and “firstdetection area SRY1” represents the area of calculation regarding theimage data obtained by the sensor device SENM for magenta and thatregarding the image data obtained by the sensor device SENY for yellow,respectively.

Preferably, the first detection area is sufficiently large to cover therange of fluctuations in movement of the web 120 due to skew andmeandering. For example, in a case where the web 120 is expected tofluctuate about ±1.0 mm in the orthogonal direction 20 due to skew ormeandering thereof, the initial setting of the detection area (i.e., thefirst detection area) preferably have a size equal to or greater than1.0 mm. When the first detection area is large enough to cover thepotential fluctuation of the web 120, the liquid discharge apparatus 110can detect the amount of movement of the web 120 even when the skew ormeandering occurs.

Referring back to FIG. 17, at S04, the liquid discharge apparatus 110performs imaging of the web 120, for example, as illustrated in FIG. 8A.Based on the imaging at S04, at S05, the liquid discharge apparatus 110can calculate the detection result (i.e., a first detection resultcalculated using the detection area according to initial setting), suchas the position of the web 120, through correlation operation and thelike.

The detection of position at S05 can be implemented, for example, by theconfiguration illustrated in FIG. 9. The correlation operation isperformed using the image data in the first detection areas SRK1, SRC1,SRM1, and SRY1 obtained at S04. In the description below, the detectionarea is the entire image data output from the imaging unit 16A or 16B.

FIG. 19 illustrates an example of skew of the recording medium, which inthe present embodiment is the web 120. Specifically, the web 120 isconveyed at an angle relative to the conveyance direction 10.Hereinafter, the web being in the illustrated state is referred to as askew web 121.

It is assumed that, initially, a given position (hereinafter “detectedposition PT”) is detected in the first detection area SRK1 of the sensordevice SENK for black. After the detection in the first detection areaSRK1, as the skew web 121 is conveyed in the conveyance direction 10,the detected position PT moves from the first detection area SRK1 forblack to the first detection area SRC1 for cyan.

In the case of the skew web 121 illustrated in FIG. 19, the detectedposition PT in the first detection area SRC1 is shifted from thedetected position PT in the first detection area SRK1 in the orthogonaldirection 20.

The detected position PT may be different between the first detectionarea SRC1 and the first detection area SRK1 also in the conveyancedirection 10.

Then, the liquid discharge apparatus 110 performs the correlationoperation to locate the detected position PT in each of the firstdetection areas SRK1 and SRC1. Note that the detection result obtainedhere is, for example, an amount of deviation of color superimposed on areference color or respective coordinate values in the first detectionareas. Based on the detection result, the liquid discharge apparatus 110can determine the degree of fluctuation of the position of the skew web121 (i.e., the amount of displacement). Note that the position of thedetected position PT can be detected multiple number of times to obtainthe detection result. In other words, the detection result can be anaverage or moving average.

Referring back to FIG. 17, at S06, the setting unit 58 sets a seconddetection area. That is, the setting unit 58 changes the position, size,or range of the detection area from the initial setting (i.e., the firstdetection area). At S06, the setting unit 58 sets the second detectionarea for example, as illustrated in FIG. 20.

Compared with FIG. 19, in FIG. 20, the first detection areas SRK1, SRC1,SRM1, and SRY1 are replaced with second detection areas SRK2, SRC2,SRM2, and SRY2.

The second detection area of the detection by the sensor device ispreferably narrower than the first detection area. In this example, theliquid discharge apparatus 110 performs imaging in the second detectionarea reduced from the first detection area. Narrowing the detection areais advantageous in improving the accuracy in detecting the position ofthe detected position PT and improving the accuracy in detecting theamount of displacement of the web 120.

Additionally, respective center positions SCK, SCC, SCM, and SCY (alsocollectively “center positions SC”) of the second detection areas SRK2,SRC2, SRM2, and SRY2 can be different from respective center positionsof the first detection areas SRK1, SRC1, SRM1, and SRY1.

Specifically, the liquid discharge apparatus 110 sets the centerposition SC of each second detection area to the position defined by theresult obtained by the correlation operation. Alternatively, the centerposition SC of the second detection area can different from the positiondefined by the result obtained by the correlation operation.

In this example, at S05, the liquid discharge apparatus 110 uses thedetected position PT detected inside the first detection area SRK1 forblack illustrated in FIG. 19, as the center position SCK for black.Similarly, at S05, the liquid discharge apparatus 110 uses the detectedposition PT detected inside the first detection area SRC1 for cyan, asthe center position SCC for cyan. Similarly, the liquid dischargeapparatus 110 uses the detected position PT detected inside the firstdetection area SRM1 and that detected inside the first detection areaSRY1, as the center position SCC for magenta and the center position SCYfor yellow, respectively.

Setting the center position SC as described above increase theprobability that the detected position PT appears at or near the centerof the image even in the case of the skew web 121. Accordingly, suchsetting increases the probability that the detected position PT at ornear the center of the image.

As described above, the liquid discharge apparatus 110 sets the seconddetection area in accordance with the skew state of the skew web 121.

Referring back to FIG. 17, at S07, the control circuit 152 (in thehardware configuration illustrated in FIG. 6) sets the irradiated areain the web 120, irradiated by the light source LG, for example, asillustrated in FIG. 21. In the software configuration illustrated inFIG. 8A, the adjusting unit 55F controls the light source controller 56A(or 56B) to set the irradiated area.

The liquid discharge apparatus 110 includes the light source LGincluding a plurality of light-emitting elements. The term “irradiatedarea” represents the range of the web 120 irradiated with the lightemitted from the light source LG.

Specifically, the light source LG includes a plurality of laser diodesarranged in the conveyance direction 10 and the orthogonal direction 20,and for example, evenly spaced. Accordingly, the light source LGpreferably has a capability to individually turn on and off theplurality of laser diodes to change the size of the irradiated area. Thelight-emitting elements of the light source LG are preferably configurednot to cancel a speckle generated by another one of the light-emittingelements. However, this limitation does not apply to a case where thesurface data is not a speckle pattern.

In the initial setting, the liquid discharge apparatus 110 sets theirradiated area to accommodate the first detection area, that is, toinclude the first detection area SRK1, SRC1, SRM1, or SRY1 asillustrated in (a) in FIG. 21.

When the second detection area is set as illustrated in FIG. 20, theliquid discharge apparatus 110 changes the irradiated area in accordancetherewith, to a range including the second detection area SRK2, SRC2,SRM2, or SRY2 as illustrated in (b) in FIG. 21 (at S07 in FIG. 17).

In the case where the first detection area is narrowed to the seconddetection area, the irradiated area is narrowed similarly. Since theirradiated area is narrowed, the light source LG can brighten the seconddetection area for imaging.

Referring back to FIG. 17, at S08, the liquid discharge apparatus 110increments the counter value N by one (N=N+1, that is, N=2) and performssecond time processing.

At S09, the liquid discharge apparatus 110 determines whether thecounter value N is “2”. When the counter value N is “2”, that is, theprocessing including the detection area setting is second time (Yes atS09), the process proceeds to Step S10. When the counter value N is not“2”, that is, the processing is not the second time (No at S09), theprocess proceeds to Step S15.

At S10, the liquid discharge apparatus performs imaging, for example,similar to S04.

At S11, the liquid discharge apparatus 110 calculates the detectionresult (i.e., a second detection result calculated using the seconddetection area according to the first detection result), such as theposition of the web 120, through correlation operation and the like, forexample, similar to S05.

Similar to the first time processing, in the second time processing andsubsequent processing, the liquid discharge apparatus 110 detects theposition through correlation operation based on the detection area as inSteps S10 and S11.

At S12, the setting unit 58 sets a third detection area. That is, thesetting unit 58 changes the position, size, or range of the detectionarea from the first and second detection areas. At S12, the setting unit58 sets the third detection area for example, as follows.

With reference to FIG. 22, descriptions are given below of the settingof the third detection area by the liquid discharge apparatus 110according to the present embodiment. Compared with FIG. 20, in FIG. 22,the second detection areas SRK2, SRC2, SRM2, and SRY2 are replaced withthird detection areas SRK3, SRC3, SRM3, and SRY3.

The third detection area detected by the sensor device is preferablynarrower than the second detection area. In this example, the liquiddischarge apparatus 110 performs imaging in the third detection areareduced from the second detection area.

As described above, the liquid discharge apparatus 110 narrows thesecond detection area to the third detection area. Note that, theposition can be changed in setting the third detection area.

Referring back to FIG. 17, at S13, the liquid discharge apparatus 110sets the irradiated area, for example, similar to Step S07. The liquiddischarge apparatus 110 sets the irradiated area in accordance with thesize and position of the third detection area to include the thirddetection area.

[0C0]

At S14, the liquid discharge apparatus increments the counter value N byone (N=N+1) and sets the counter value N to “3”. Then, the determinationis “No” at S09, and the third time processing is performed.

At S15, the liquid discharge apparatus 110 performs imaging, forexample, similar to S04.

At S16, the liquid discharge apparatus 110 detects the position of theweb 120 through correlation operation and the like, for example, similarto S05.

At S17, the setting unit 58 sets a fourth detection area. That is, atS17, the setting unit 58 changes the position, size, or range of thedetection area from that of the first to third detection areas. At S17,the setting unit 58 sets the fourth detection area for example,illustrated in FIG. 23.

Compared with FIG. 22, in FIG. 23, the third detection areas SRK3, SRC3,SRM3, and SRY3 are replaced with fourth detection areas SRK4, SRC4,SRM4, and SRY4.

The fourth detection area is preferably set so that the area used indetection by the sensor device is narrower than the third detectionarea. In this example, the liquid discharge apparatus 110 reduces theimage size of the fourth detection area from the image size of the thirddetection area.

As described above, the liquid discharge apparatus 110 narrows the thirddetection area to the fourth detection area. Note that, in setting thefourth detection area, the position can be changed.

Referring back to FIG. 17, at S18, the liquid discharge apparatus 110sets the irradiated area, for example, similar to Step S07. The liquiddischarge apparatus 110 sets the irradiated area in accordance with thesize and position of the fourth detection area to include the fourthdetection area.

As described above, setting of the detection areas and the like isperformed in preparation before image formation is performed at S19.

Note that the timings of imaging at S04, S10, and S15 are not limited tothose illustrated in FIG. 14. For example, the imaging may be performedperiodically based on a predetermined period. Then, the liquid dischargeapparatus 110 can perform the correlation operation at a predeterminedtiming based on the images taken periodically.

At S19, the liquid discharge apparatus 110 performs image formation.Then, the conveyed object detector 600 detects the pattern on the web120, with the fourth detection area set in the third time processing,that is, last setting. Based on the result of detection of the pattern,the liquid discharge apparatus 110 adjusts the discharge position ofliquid and then discharges the liquid. Such detection and adjustment ofthe discharge position are performed during a print job. To adjust thedischarge position of liquid, based on the result of detection of thepattern, for example, the liquid discharge head unit 210 is moved, orthe timing of discharge of liquid is adjusted. Specifically, the liquiddischarge apparatus 110 calculates the amount of displacement of the webas follows and moves the liquid discharge head unit 210.

Note that the liquid discharge apparatus 110 performs the detectionusing the fourth detection area and adjustment of the discharge positionalso during image formation. For example, the detection using the fourthdetection area and adjustment of the discharge position are performedperiodically based on a predetermined period. This configuration isadvantageous in that, even when the position of the web 120 fluctuatesas illustrated in FIG. 12B, the liquid discharge apparatus 110 candetects the fluctuation of the web 120 and adjust the discharge positionof liquid. Accordingly, the accuracy of the landing position of liquidcan improve.

With the improved accuracy of landing position, the liquid dischargeapparatus 110 can prevent the misalignment in color superimpositionillustrated in FIG. 13 to improve image quality.

FIG. 24 is a timing chart of calculation of the amount of displacementof the conveyed object, performed by the liquid discharge apparatus 110according to the present embodiment. As illustrated in FIG. 22, thecalculator 53F (illustrated in FIG. 8A) calculates the amount ofdisplacement of the web 120 based on the result of detection using theplurality of fourth detection areas. Specifically, the calculator 53Foutputs the result of calculation indicating the displacement based onfirst and second detection results SD1 and SD2. In the illustratedexample, the upstream sensor device outputs the first detection resultSD1, and downstream sensor device outputs the second detection resultSD2.

The amount of displacement is calculated for each liquid discharge headunit 210. Descriptions are given below of calculation of displacement ofthe web 120 for adjusting the cyan liquid discharge head unit 210C(illustrated in FIG. 2). In this example, the displacement of the web120 is calculated based on the detection result generated by the sensordevice SENC (illustrated in FIG. 2) and that by the sensor device SENKdisposed upstream from and next to the sensor device SENC. In FIG. 24,the first detection result SD1 is generated by the sensor device SENK,and the second detection result SD2 is generated by the sensor deviceSENC.

When L2 represents the distance (interval) between the sensor deviceSENK and the sensor device SENC, V represents the conveyance speeddetected by the speed detection circuit SCR, and T2 represents the timefor the web 120 (conveyed object) to be conveyed from the sensor deviceSENK to the sensor device SENC, the time T2 is calculated as “T2=L2/V”.

Further, when A represents a sampling interval of the sensor devices andn represents the number of times of sampling performed while the web 120travels from the sensor device SENK to the sensor device SENC, thenumber of times of sampling “n” is calculated as “n=T2/A”.

The calculation result is referred to as a displacement ΔX. For example,in a case of a detection cycle “0” in FIG. 24, the first detectionresult SD1 before the travel time T2 is compared with the seconddetection result SD2 at the detection cycle “0”, to calculate thedisplacement ΔX of the web 120. This calculation is expressed asΔX=X2(0)−X1(n). In the arrangement in which the position of the sensordevice is between the liquid landing position and the first roller CR1,the liquid discharge apparatus 110 calculates an expected amount ofdisplacement of the recording medium till the recording medium reachesthe sensor device. Then, the liquid discharge apparatus drives theactuator.

Subsequently, the liquid discharge apparatus 110 controls the secondactuator AC2 (illustrated in FIG. 4) to move the liquid discharge headunit 210C (illustrated in FIG. 2) in the orthogonal direction 20, tocompensate for the displacement ΔX. With this operation, even when theposition of the conveyed object changes in the orthogonal direction 20,the liquid discharge apparatus 110 can form an image on the conveyedobject with a high accuracy. Further, as the displacement is calculatedbased on the two detection results, that is, the detection resultsgenerated by the two different sensor devices, the displacement of theconveyed object can be calculated without multiplying the position dataof the sensor devices. This operation can suppress the accumulation ofdetection errors by the sensor devices SN.

The amount of displacement can be calculated similarly for other liquiddischarge head units 210. The first detection result SD1 generated bythe second sensor device SEN2 (illustrated in FIG. 2) and the seconddetection result SD2 generated by the sensor device SENK are used tocalculate the displacement of the web 120 for adjusting the black liquiddischarge head unit 210K (illustrated in FIG. 2). The first detectionresult SD1 generated by the sensor device SENC and the second detectionresult SD2 generated by the sensor device SENM are used to calculate thedisplacement of the web 120 for adjusting the magenta liquid dischargehead unit 210M (illustrated in FIG. 2). The first detection result SD1generated by the sensor device SENM and the second detection result SD2generated by the sensor device SENY are used to calculate thedisplacement of the web 120 for adjusting the yellow liquid dischargehead unit 210Y (illustrated in FIG. 2).

The sensor device to generate the detection result SD1 is not limited tothe sensor device SEN disposed next to and upstream from the liquiddischarge head unit 210 to be moved. That is, the first detection resultSD1 can be generated by any of the sensor devices disposed upstream fromthe liquid discharge head unit 210 to be moved. For example, any one ofthe second sensor device SEN2 and the sensor devices SENK and SENC cangenerate the first detection result SD1 to calculate the displacement ofthe web 120 for adjusting the yellow liquid discharge head unit 210Y.

By contrast, the second detection result SD2 is preferably generated bythe sensor device SEN closest to the liquid discharge head unit 210 tobe moved.

Alternatively, the displacement of the conveyed object can be calculatedbased on three or more detection results.

Based on the displacement of the web 120 thus calculated based on aplurality of detection results, the liquid discharge head unit 210 ismoved, and the liquid is discharged onto the web 120 (i.e., therecording medium) to form an image thereon.

Referring back to FIG. 17, the detection area is preferably reducedstepwise from the initial setting, for example, in three steps. Notethat the number of steps of reduction of the detection area (the largestvalue of the count value N) can be preset in the liquid dischargeapparatus 110. The number of steps of reduction of the detection area isnot limited to three. The image size to be set in each reduction of thedetection area can be preset in the liquid discharge apparatus 110.

As described above, in the initial setting, the detection area is set tothe first detection area that is a largest size detectable by the sensordevice. In the first time processing, the detection area is set to thesecond detection area that is smaller than the first detection area andlarger than the third detection area. In the second time processing, thedetection area is set to the third detection area that is smaller thanthe second detection area and larger than the fourth detection area. Atthe last, in the third time processing, the detection area is set to thefourth detection area that is smaller than the third detection area,that is, smallest of the detection areas used. Gradually narrowing thedetection area in such a manner is preferred.

For example, the first detection area is 2 mm in the conveyancedirection 10 and 6 mm in the orthogonal direction 20. The fourthdetection area is 1 mm in the conveyance direction 10 and 1 mm in theorthogonal direction 20. The length of the detection area in theconveyance direction 10 and that in the orthogonal direction 20 can beidentical or different.

Alternatively, the fourth detection area can be 2 mm in the conveyancedirection 10 and 2 mm in the orthogonal direction 20. Thus, the firstdetection area and the fourth detection area can be identical in lengthin the orthogonal direction 20.

The size of the detection area is preferably identical among the fourcolors. In other words, the respective images taken in the firstdetection areas SRK1, SRC1, SRM1, and SRY1 for black, cyan, magenta, andyellow are preferably identical in size. When the images are same insize, the processing such as the correlation operation is easier.Similarly, each of the second, third, and fourth detection areas ispreferably identical among the four colors.

To set the detection area, for example, the amount of data read out fromthe sensor device is set, or a portion of the image output from thesensor device is cut out. The setting unit 58 (58A or 58 b) is mountedin the imaging unit 16 as illustrated in FIG. 8A when the amount of dataread out is set. Alternatively, the setting unit 58 is mounted in theimaging controller 14 as illustrated in FIG. 8B when the range of cutoutis set. Narrowing the range of reading out from the sensor device isadvantageous in reducing the data size read out from the sensor device.The amount of calculation by the calculator 53F can be reduced in thesetting the detection area in any of the first time, second time, andthird time processing.

As the detection area is changed, preferably the irradiated area is setin accordance with the detection area as set at S07, S13, and S18.

Specifically, in a case where the detection area is relatively large,the liquid discharge apparatus 110 may slow down the speed of conveyanceof the web 120 in the conveyance direction 10. When the speed ofconveyance is slow, the liquid discharge apparatus 110 can lowerso-called frame rate to increase the period of imaging performedperiodically. Generally, the duration of exposure can be made long whenthe frame rate is low.

Additionally, the frame rate is set in accordance with, for example, thespeed of image formation. For example, the frame rate is set in a rangefrom 50 to 800 frames per second (fps). When the speed of imageformation is relatively fast, generally, the speed of conveyance of theweb is slowed, and the frame rate is increased.

Further, at the first time, generally, the duration of exposure can beset long. Accordingly, in the imaging at the first time, generally abright image can be obtained even under a relatively dark imagingcondition. Therefore, in the first time processing, the intensity oflight emitted from the light source LG is preferably reduced to avoidsaturation of image due to the light.

By contrast, when the speed of conveyance is fast, preferably, the framerate is preferably increased to increase the number of times of imagingperformed per unit time. Generally, the duration of exposure is shortwhen the frame rate is high. Accordingly, for example, in the fourthtime imaging, the duration of exposure is shorter than that in the firsttime imaging. When the duration of exposure is short, the image obtainedmay be dark. Accordingly, in the second time processing and subsequentprocessing, the irradiated area is set (narrowed), for example, asillustrated in FIG. 21. Thus, the liquid discharge apparatus 110 narrowsthe irradiated area and increase the intensity of light. Under such alighting condition, the liquid discharge apparatus 110 can obtain abright image even when the duration of exposure is short.

[Variation]

Note that, alternatively, the detecting unit 110F10 can perform imagingtwice with an identical sensor device and compare the images obtained bythe first imaging and second imaging, to output the detection resultindicating at least one of the position, speed of movement, and amountof movement of the web 120.

One or more of aspects of this disclosure can adapt to a conveyancesystem such as a liquid discharge system including at least one liquiddischarge apparatus. For example, the liquid discharge head unit 210Kand the liquid discharge head unit 210C are housed in one case as oneapparatus, and the liquid discharge head unit 210M and the liquiddischarge head unit 210Y are housed in another case as anotherapparatus. The liquid discharge system includes the two apparatuses.

Further, one or more of aspects of this disclosure can adapt to a liquiddischarge system to discharge liquid other than ink. For example, theliquid is a recording liquid of another type or a fixing solution. Inother words, aspects of this disclosure can adapt to a liquid dischargeapparatus to discharge liquid other than ink and a system including sucha liquid discharge apparatus.

The liquid discharge apparatus (or system) to which at least one aspectof this disclosure is applicable is not limited to apparatuses to formimages. The articles produced can be, for example, a three-dimensionalobject (a 3D-fabricated object).

[Variation 1]

Note that, a single support can double as the first and second supports.An example configuration of the first and second supports is describedbelow.

FIG. 25 is a schematic view of a liquid discharge apparatus according toVariation 1. This configuration differs from the configurationillustrated in FIG. 2 regarding the locations of the first support andthe second support. As illustrated in this drawing, the liquid dischargeapparatus 110 includes supports RL1, RL2, RL3, RL4, and RL5, serving asthe first and second supports. In other words, one support can double asthe second support (e.g., the conveyance roller CR2K in FIG. 2) disposedupstream from the downstream one of adjacent two liquid discharge headunits and the first support (e.g., the conveyance roller CR1C in FIG. 2)disposed upstream from the upstream one of the adjacent two liquiddischarge head units. Note that, the support according to the Variation,which doubles as the first and second supports, can be either a rolleror a curved plate.

[Variation 2]

For example, the conveyance device according to this disclosure can be adevice to perform operation, such as reading, relative to the conveyedobject.

FIG. 26 is a schematic diagram of a conveyance device according toVariation 2. In the example described below, the web 120 is conveyedfrom the left to the right in FIG. 26.

In this example, the conveyance device includes a head unit including acontact image sensor (CIS) head.

The head unit includes at least one CIS head. When head unit includes aplurality of CIS heads, the CIS heads are arranged in the orthogonaldirection 20. In the illustrated example, the conveyance device includestwo head units HD1 and HD2 (also collectively “head units HD”). Thenumber of head units is not limited two but can be three or more.

As illustrated in FIG. 26, the head units HD1 and HD2 each include atleast one CIS head. Although a description is made below of aconfiguration in which each head unit HD includes the one CIS head,alternatively, a plurality of CIS heads can be arranged in a zigzagmanner, for example, with each two CIS heads staggered.

The head units HD and HD2 construct a scanner to read an image on thesurface of the web 120 and output image data representing the image thusread. The conveyance device can combine pieces of image data output fromthe head units HD together to generate an image combined in theorthogonal direction 20.

The conveyance device illustrated in FIG. 26 includes the controller520, and the actuator controllers CTL1 and CTL2. The controller 520 andthe actuator controllers CTL1 and CTL2 are information processingapparatuses and, specifically, have hardware including a processor, acontrol device, a memory device, and an interface implemented by a CPU,an electric circuit, or a combination thereof. Note that the controller520 and the actuator controllers CTL1 and CTL2 can be implemented byeither a plurality of devices or a single device.

The head units are provided with the first sensor device SEN1 and thesecond sensor device SEN2 (also collectively “sensor devices SEN”),respectively. The conveyance device detects, with the sensor devicesSEN, the surface data of the web 120 and detects at least one of therelative position, speed of movement, and the amount of movement of theweb 120 among a plurality of detection results.

For the two head units HD1 and HD2, a plurality of rollers is provided.As illustrated in the drawing, for example, a first roller R1 and asecond roller R2 are respectively disposed upstream and downstream fromthe two head units HD1 and HD2.

The sensor device SEN disposed in an inter-roller range INT between thefirst and second rollers R1 and R2 can detect the web 120 at a positionclose to the operation position. Since the moving speed is relativelystable in the inter-roller range INT, the conveyance device canaccurately detect at least one of the relative position, speed ofmovement, and the amount of movement of the conveyed object among aplurality of detection results.

Preferably, in each inter-roller ranges INT1, the sensor device SEN isdisposed closer to the first roller R1 than the operation position is.That is, preferably, the sensor device SEN performs the detection at aposition upstream from the operation position of the head unit HD. InFIG. 26, the first sensor device SEN1 is preferably disposed between theoperation position of the head unit HD and the first roller R1, that is,in a first upstream range INT1 in FIG. 26.

Similarly, the second sensor device SEN2 is preferably disposed betweenthe operation position of the head unit HD2 and the first roller R1,that is, in a second upstream range INT2 in FIG. 26.

When the first and second sensor devices SEN1 and SEN2 are disposed inthe first and second upstream ranges INT1 and INT2, respectively, theconveyance device can detect the conveyed object with a high accuracy.The sensor devices SEN disposed upstream from the operation position ofthe head unit HD can detect the surface data of the conveyed object at aposition upstream from the operation position. Then, based on thedetection result, the conveyance device can calculate the timing ofoperation by the head unit HD, the amount by which the head unit HD isto be moved, or both in at least one of the orthogonal direction 20 andthe conveyance direction 10. In other words, in a period from when theposition of a given portion of the web 120 (conveyed object) is detectedon the upstream side to when the detected portion of the web 120 reachesthe operation position, the operation timing is calculated or the headunit HD is moved. Therefore, the conveyance device can change theoperation position with high accuracy.

If the sensor device SEN is disposed directly below the head unit HD, insome cases, depending on the calculation of operation timing or time formoving the head unit HD, the start of operation may be delayed.Accordingly, disposing the sensor device SEN upstream from the operationposition can minimize the delay in operation of the head unit.Additionally, there may be a restriction on disposing the sensor deviceSEN adjacent to the operation position, that is, directly below the headunit HD. Accordingly, the location of sensor device is preferably closerto the first roller R1 than the operation position, that is, upstreamfrom the ink operation position.

The web 120 may be irradiated with light in both of the operation by thehead unit HD and detection by the sensor device SEN. In particular, whenthe web 120 has a high degree of transparency, the light for one of theoperation and the detection may disturb the other. In such a case,disposing the sensor device SEN and the head unit HD on an identicaloptical axis is undesirable.

By contrast, when the transparency of the web 120 is lower, the sensordevice SEN can be directly below the head unit HD. In the illustratedexample, the position directly below the head unit HD is on the backside of the operation position. In other words, in some cases, theoperation position and the location of sensor device are almostidentical in the conveyance direction 10, and the operation is made onone side (e.g., front side) of the web 120 and the other side of the web120 (e.g., back side) is detected by the sensor device SEN.

The sensor device SEN disposed directly below the head unit HD canaccurately detect the amount of movement of the conveyed object directlybelow the head unit HD. Therefore, in a case where the light for one ofthe operation and the detection does not disturb the other and the speedof control action is relatively fast, the sensor device SEN ispreferably disposed closer to the position directly below the head unitHD. However, the location of sensor device is not limited to a positiondirectly below the head unit HD, and similar calculation is feasiblewhen the sensor device SEN is disposed otherwise.

Alternatively, in a configuration in which error is tolerable, thelocation of sensor device can be almost directly below the head unit HD,or downstream from the position directly below the head unit HD in theinter-roller range INT.

[Variation 3]

The liquid discharge apparatus 110 (or the conveyance device) can conveya belt as the conveyed object.

FIG. 27 is a schematic diagram of a liquid discharge apparatus accordingto Variation 3. In this example, head units 350C, 350M, 350Y, and 350Kdischarge ink droplets to form an image on the outer side of the loop ofa transfer belt 328. The head units 350C, 350M, 350Y, and 350K are alsocollectively referred to as head units 350.

A drier 370 dries an image formed on the transfer belt 328 into a film.

Then, at a transfer position where the transfer belt 328 faces atransfer roller 360, the liquid discharge apparatus 110 transfers theimage in the form of film, conveyed on the transfer belt 328, onto asheet P.

Additionally, a cleaning roller 323 cleans the surface of the transferbelt 328 after the transfer.

In the liquid discharge apparatus 110 illustrated in FIG. 27, the headunits 350C, 350M, 350Y, and 350K, the drier, the cleaning roller 323,and the transfer roller 360 are disposed around the transfer belt 328.

In this example, the transfer belt 328 is stretched taut around adriving roller 321, an opposing roller 322 (a transfer-backup roller),four shape-keeping rollers 324, and eight support rollers 325C1, 352C2,325M1, 325M2, 325Y1, 325Y2, 325K1, and 325K2. As the driving roller 321rotates driven by a belt driving motor 327, the transfer belt 328rotates in the conveyance direction 10 indicated an arrow illustrated inFIG. 27.

The eight support rollers 325C1, 352C2, 325M1, 325M2, 325Y1, 325Y2,325K1, and 325K2, disposed opposite the head units 350, keep thetransfer belt 328 taut when the head units 350C, 350M, 350Y, and 350Kdischarge ink droplets. A transfer motor 331 drives the transfer roller360.

Further, a sensor device 332C is disposed between the support rollers325C1 and 325C2 and upstream from the ink discharge position of the headunit 350C in the conveyance direction 10 in which the transfer belt 328rotates. The sensor device 332C includes a speckle sensor,

which is an example to take an image of the surface of the transfer belt328. Similar to the position of the sensor device 332C relative to thesupport rollers 325C1 and 325C2 and the head unit 350C, the sensordevice 332M is disposed for the head unit 350M.

For the head units 350M, 350Y, and 350K, actuators 333M, 333Y, and 333Kare provided, respectively. The actuator 333M moves the head unit 350Min the direction orthogonal to the conveyance direction 10 in which thetransfer belt 328 rotates. Similarly, the actuators 333Y and 333K movethe head units 350Y and 350K, respectively, in the direction orthogonalto the conveyance direction 10 in which the transfer belt 328 rotates.

A control board 340 detects the amount of movement of the transfer belt328 in the direction orthogonal to the conveyance direction 10 and thatin the conveyance direction, based on the image data obtained from thesensor devices 332C, 332M, 332Y, and 332K. Additionally, according tothe amount of movement of the transfer belt 328 in the orthogonaldirection, the control board 340 controls the actuators 333M, 333Y, and333K to move the head units 350M, 350Y, and 350K in the orthogonaldirection. Additionally, according to the amount of movement of thetransfer belt 328 in the conveyance direction 10, the control board 340controls the timing of liquid discharge from the head units 350M, 350Y,and 350K.

The control board 340 outputs driving signals to the belt driving motor327 and the transfer motor 331.

Variation 3 can attain the following effects.

When the transfer belt 328 moves in the direction orthogonal to thedirection in which the transfer belt 328 is driven by the driving roller321 during driving of the transfer belt 328, the liquid dischargeapparatus 110 can move the head units 350M, 350Y, and 350K in theorthogonal direction, corresponding to the amount of movement detected.Accordingly, the liquid discharge apparatus 110 can form a high-qualityimage on the transfer belt 328.

When the amount by which the transfer belt 328 rotates in the directiondriven by the driving roller 321 is different from a supposed amount,the liquid discharge apparatus 110 can change the timing of liquiddischarge from the head units 350M, 350Y, and 350K in response to theamount of rotation detected. Accordingly, the liquid discharge apparatus110 can form a high-quality image on the transfer belt 328.

In the above-described example, the amount of movement of the transferbelt 328 in the direction orthogonal to the conveyance direction 10 andthat in the conveyance direction are calculated based on the image dataobtained from the sensor devices 332C, 332M, 332Y, and 332K.Alternatively, one of the amounts of movements can be calculated.

Although the head unit 350C does not includes an actuator in theabove-described example, alternatively, an actuator can be provided.Then, the head unit 350C is moved in the direction orthogonal to theconveyance direction 10, thereby adjusting the position of the head unit350C in the orthogonal direction at the time of image transfer from thetransfer belt 328 onto the sheet P.

Although a plurality of head units is used to form an image on thetransfer belt 328 in the example described above, alternatively, theoperation described above can adopt to forming an image using one headunit.

The conveyed object is not limited to recording media such as papersheets but can be any material to which liquid adheres, eventemporarily. Examples of the material to which liquid adheres includepaper, thread, fiber, cloth, leather, metal, plastic, glass, wood,ceramics, and a combination thereof.

Further, aspects of this disclosure can adapt to any apparatus toperform an operation or processing on a conveyed object, using a linehead unit including heads lined in a direction orthogonal to thedirection of conveyance of the conveyed object.

For example, aspects of this disclosure can adapt to a conveyanceapparatus that conveys a substrate (conveyed object) and includes alaser head to perform laser patterning on the substrate. A plurality ofsuch laser heads can be lined in the direction orthogonal to thedirection of conveyance of the substrate. The conveyance device detectsthe position of the substrate and moves the head based on the detectionresult. In this case, the position at which the laser lands on thesubstrate is the operation position of the head.

The number of the head units is not necessarily to two or more. Aspectsof this disclosure can adapt to a device configured to keep operation atto a reference position, on a conveyed object.

Further, one or more of aspects of this disclosure can be embodied as amethod performed by a computer of a conveyance device, an informationprocessing apparatus, or the combination thereof to cause the apparatusto discharge liquid, and at least a portion of the method can beimplemented by a program.

The above-described embodiments are illustrative and do not limit thepresent invention. Thus, numerous additional modifications andvariations are possible in light of the above teachings. For example,elements and/or features of different illustrative embodiments may becombined with each other and/or substituted for each other within thescope of the present invention.

Each of the functions of the described embodiments may be implemented byone or more processing circuits or circuitry. Processing circuitryincludes a programmed processor, as a processor includes circuitry. Aprocessing circuit also includes devices such as an application specificintegrated circuit (ASIC), digital signal processor (DSP), fieldprogrammable gate array (FPGA), and conventional circuit componentsarranged to perform the recited functions.

What is claimed is:
 1. A conveyance device comprising: a conveyor toconvey a conveyed object in a conveyance direction; at least one headunit to perform an operation on the conveyed object; a sensor to obtainsurface data in a region of the conveyed object, the sensor provided foreach of the at least one head unit; and at least one processorconfigured to: calculate a first detection result including at least oneof a position, a speed of movement, and an amount of movement of theconveyed object based on the surface data obtained by the sensor; set adetection area that is smaller than the region based on the firstdetection result, calculate a second detection result including at leastone of the position, the speed of movement, and the amount of movementof the conveyed object, using the detection area according to the firstdetection result; and control the operation of the at least one headunit based on the second detection result.
 2. The conveyance deviceaccording to claim 1, wherein the detection area is a range of thesurface data to be used in calculation of the first detection result andthe second detection result, and wherein the at least one processor isconfigured to set a center position of the detection area based on thefirst detection result.
 3. The conveyance device according to claim 1,further comprising a light source to irradiate an area including thedetection area, wherein the at least one processor is configured to setan irradiated area irradiated by the light source, based on firstdetection result and the second detection result.
 4. The conveyancedevice according to claim 3, wherein the at least one processor isconfigured to set an intensity of light emitted from the light source.5. The conveyance device according to claim 1, wherein the at least oneprocessor is configured to set the detection area stepwise.
 6. Theconveyance device according to claim 1, further comprising: a firstsupport disposed upstream from an operation position of each of the atleast one head unit in the conveyance direction; and a second supportdisposed downstream from the operation position of each of the at leastone head unit in the conveyance direction, wherein the sensor isdisposed between the first support and the second support.
 7. Theconveyance device according to claim 6, wherein the sensor is disposedbetween each of the at least one head unit and the first support in theconveyance direction.
 8. The conveyance device according claim 1,wherein the sensor is an optical sensor.
 9. The conveyance deviceaccording to claim 1, wherein the surface data represents a pattern ofthe conveyed object.
 10. The conveyance device according to claim 9,wherein, based on the surface data detected at two or more differenttime points, the at least one processor is configured to calculate thefirst detection result and the second detection result for each of theat least one head unit.
 11. The conveyance device according to claim 9,wherein the pattern is generated by interference of light reflected on arugged shape of the conveyed object, and wherein the at least oneprocessor is configured to obtain the first detection result and thesecond detection result based on an image of the pattern, obtained bythe sensor.
 12. The conveyance device according to claim 1, wherein theat least one head unit includes a liquid discharge head to perform, asthe operation, image formation on the conveyed object.
 13. Theconveyance device according to claim 1, wherein the conveyed object is acontinuous sheet extending in the conveyance direction.
 14. Theconveyance device according to claim 1, further comprising a head movingdevice to move the at least one head unit, wherein the at least oneprocessor is configured to control the head moving device based on thesecond detection result.
 15. The conveyance device according to claim 1,wherein the at least one processor is configured to control timing ofthe operation performed by each of the at least one head unit based onthe second detection result.
 16. The conveyance device according toclaim 15, further comprising a gauge to measure an amount of movement ofthe conveyed object, wherein the at least one processor is configured tocontrol the at least one head unit based on the amount of movementmeasured by the gauge and the second detection result.
 17. A conveyancesystem comprising: a plurality of conveyance devices each of whichincluding: a conveyor to convey a conveyed object in a conveyancedirection; at least one head unit to perform an operation on theconveyed object; and a sensor to obtain surface data in a region of theconveyed object, the sensor provided for each of the at least one headunit; and at least one processor configured to: calculate a firstdetection result including at least one of a position, a speed ofmovement, and an amount of movement of the conveyed object based on thesurface data obtained by the sensor; set a detection area that issmaller than the region based on the first detection result, calculate asecond detection result using the detection area according to the firstdetection result; and control operation of the at least one head unitbased on the second detection result.
 18. A method for controlling ahead to perform an operation on a conveyed object, the methodcomprising: obtaining surface data in a region of the conveyed object;calculating a first detection result including at least one of aposition, a speed of movement, and an amount of movement of the conveyedobject based on the surface data; setting a detection area that issmaller than the region used based on the first detection result;calculating a second detection result including at least one of theposition, the speed of movement, and the amount of movement of theconveyed object, using the detection area according to the firstdetection result; and controlling the operation of the head based on thesecond detection result.